Java IRC applets are dreadful, as well is Mibbit for that matter, you should definitely consider switching to LightIRC (Flash) or Iris (Python using the twisted frame work). LightIRC is a lighter (excuse the pun) faster and cleaner client which is easier to navigate the Java or Mibbit, while Iris has some cool features, like a channel cloud rather than a list, as well as the ability to add tabs to the chat box itself.